Sensing shear force has received considerable interest in recent times for a number of practical reasons. Piezoresistive materials have applicability since the resistive properties of a material may change due to shear force. Optical means of sensing shear force are possible as light and the lens through which it passes is changed due to shear stress. Another way shear force sensing is commonly accomplished is by using ultrasonic transducers, and a graphical rendering of such stresses is possible via a computer.
The motivation for knowing shear forces has much utility. In robotics, it allows the determination of the existing friction in picking up objects. It enables the user to ascertain the required force to lift objects of various densities. If an object contains a fabric, this information can be conveyed to a remote operator through the shear force sensing mechanism. For all types of grasping and manipulation, measurement of the forces and pressure points is important when humans contact clothing, shoes, boots, sporting equipment, industrial implements (hand tools, etc), and for determination of balance and gait analysis for athletic training. The applications also include medical treatment and rehabilitation, for accelerometers and numerous other purposes where an additional dimension of force needs to be properly sensed and fed back to the user.
To define more precisely how the term xe2x80x9cshear forcexe2x80x9d is to be used, herein, FIG. 1 illustrates a force vector V, shown at 103, acting on a mass, 100, at an oblique angle xcex8, 102. The vector V 103 can be decomposed into two vectors: at 104 Vn is a normal vector which acts on the mass in a direction perpendicular to the ground, and at 101 Vt, is the component of the force vector V which is transverse to the ground (shear force) and is perpendicular to the normal force. V 103 is the vector sum of Vn, 104 and Vt 101 since they act at right angles. The magnitude of V 103 can bc expressed, using the hypotenuse rule for right triangles, as:
|V|2=|Vn|2+|Vt|2xe2x80x83xe2x80x83Eq. 1
By using equation (1), the shear force term Vt can be computed.
The invention uscs micro electromechanical components in a novel configuration to allow wireless normal direction pressure transducers to be used for measurement of oblique or shear forces. The invention includes a novel cantilever bcam configuration and algorithm, the rcadings of the MEMS sensors are averaged to reduce the experimental variability, to estimate the shear stress that may occur between a human and external equipment or possibly between materials. The shear force component is calculated via the formula:
Shear Force=Vt={square root over ({overscore (V)})}23+4+ . . . +n1xe2x88x92{overscore (V)}21+2+ . . . +n2
It is therefore an object of the invention is to provide a mechanical-electrical shear force sensing apparatus.
Another object of the invention is to provide a wireless shear force sensing apparatus.
Another object of the invention to provide a mechanical-electrical shear force sensing apparatus with reduced variability.
Another object of the invention is to provide a mechanical-electrical shear force sensing apparatus operable through nonmetallic materials.
These along with other objects of the invention described in the description, claims and drawings are achieved by a sensing apparatus responsive to shear forces comprising:
a first plurality of mechanical-electrical sensing components integral with a first rectangular structure and sensing normal forces;
a second plurality of mechanical-electrical sensing components integral with a second rectangular structure adjacent and in a cantilever beam configuration to said first rectangular structure and sensing both normal and transverse forces;
microelectronic processing means for reading force data obtained by said mechanical-electrical sensing components, temperature, and individual mechanical-electrical sensing component identifying data; and
an operator interfacing external antenna transmitting power and an instructional signal to said mechanical-electrical sensing components and thereafter receiving said force, temperature and sensing component identifying data from said microelectronic processing means to determine shear force according to the relationship
Shear Force=Vt={square root over ({overscore (V)})}23+4+ . . . +n1xe2x88x92{overscore (V)}21+2+ . . . +n2